net/socks5: always close client connections after serving

Customer reported an issue where the connections were not closing, and
would instead just stay open. This commit makes it so that we close out
the connection regardless of what error we see. I've verified locally
that it fixes the issue, we should add a test for this.

Signed-off-by: Maisem Ali <maisem@tailscale.com>
(cherry picked from commit 2fb087891b)

net/socks5/socks5.go

@@ -112,11 +112,11 @@ func (s *Server) Serve(l net.Listener) error {
 			return err
 		}
 		go func() {
+			defer c.Close()
 			conn := &Conn{clientConn: c, srv: s}
 			err := conn.Run()
 			if err != nil {
 				s.logf("client connection failed: %v", err)
-				conn.clientConn.Close()
 			}
 		}()
 	}